bool isUnique(char* astr) {
	int i = 0;
	bool hash[26] = { 0 };
	while (astr[i]) {
		if (hash[astr[i] - 'a'] == 1)
			return false;
		else
			hash[astr[i] - 'a'] = 1;
		i++;
	}
	return true;
}